a phase 1/2 first-in-human trial of oral sra737 (a chk1...

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CRC CRC HGSOC NSCLC CRC CRC CRC CRC NSCLC CRC CRC CRC CRC CRC CRC NSCLC CRC CRC CRC NSCLC

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HGSOC mCRPC NSCLC HGSOC HGSOC mCRPC mCRPC NSCLC HGSOC mCRPC mCRPC HGSOC mCRPC

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PRKDCBRCA1BRCA2CDK12FANC*RAD**

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Chromatin

Mismatch Repair

6 3 100%

19 19 68%

22 21 71%

77%PI3K

FA/BRCA

HR/NHEJ

67%

RAS

CCNE

25%

50%MYC

11 9

20 NA

8 4

56%

G1/S 40%

50 33

7 5

19 13

p53 Pathway

DNA Damage Response and Repair Network

Cell Cycle Dysregulation

Oncogenic Drivers

DNA Pol

MDM2TP53RB1CDKN1A/BCDKN2A/B/CCCNE1FBXW7PARK2KRASNRASHRASMYCMYCNMYCL1PIK3CAPTENAKT1/2/3CDK12FANC*RAD**ATRBRCA1/2RAD51BRAD51CPRKDCPALB2ATMMLL2ARID1AARID1BMLH1MSH2MSH6PMS2POLD1POLE

Functional Gene Category Gene

Number of Subjects

Number of RAS Wild-Type

SubjectsDCR‡

(%)Gene Network

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CRC CRC HGSOC NSCLC CRC CRC CRC CRC NSCLC CRC CRC CRC CRC CRC CRC NSCLC CRC CRC CRC NSCLC 031-040 011-011 143-046 149-026 141-005 149-003 148-001 031-031 148-017 141-002 141-012 011-012 031-047 145-001 031-060 149-007 011-013 031-054 144-027 148-031

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HGSOC mCRPC NSCLC HGSOC HGSOC mCRPC mCRPC NSCLC HGSOC mCRPC mCRPC HGSOC mCRPC 039-057 011-002 148-015 147-019 144-031 031-093 149-015 140-021 141-017 011-010 141-022 144-029 031-053

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HGSOC HGSOC CRC Mesothelioma HGSOC CRC HGSOC HGSOC CRC HGSOC mCRPC mCRPC HGSOC HGSOC mCRPC HGSOC CRC HGSOC mCRPC HGSOC HGSOC 031-019 141-015 149-010 031-007 031-011 031-038 143-061 144-031 146-001 144-026 146-008 149-015 141-017 031-100 011-010 144-029 146-002 143-033 031-053 031-013 140-007

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• Treatment-emergent adverse events (TEAEs) werereported in 106 (99%) subjects and 97 subjects (91%) experienced at least one SRA737-related event.

• The majority of TEAEs were mild to moderate inseverity (90% Grade 1/Grade 2).

• The most common TEAEs were diarrhea (68%), nausea(66%), vomiting (51%) and fatigue (47%).

• The most common ≥ Grade 3 TEAEs were neutropeniaand disease progression (8% each), lymphocyte countdecreased (5%), infection and hyponatremia (4% each)and nausea, abdominal pain, abdominal pain upper,fatigue, AST increased, dyspnea, pleural effusion, andrash maculo-papular (3% each).

• The most common ≥ Grade 3 SRA737-related TEAEswere neutropenia (8%) and rash maculo-papular (3%).

• Six Grade 5 TEAEs were reported up to 30-dayspost last treatment; none were considered related toSRA737.

• Median duration of exposure was 2.3 cycles (range < 1to 9 cycles).

• No evidence of emergent or cumulative toxicity and/ordeclining tolerability was observed with up to 9 cyclesof SRA737 administered.

Authors and AffiliationsRuth Plummer1, Rebecca Kristeleit2, Elena Cojocaru3, Noor Haris1, Louise Carter4, Robert Jones5, Sarah Blagden6, Jeff Evans7, Tobias Arkenau8, Debashis Sarker9, Sarah Danson10, Stefan Symeonides11, Harriet Walter12, Joanita Murangira Ocen5, Manreet Randhawa7, Christian Hassig13, Mark Kowalski13, Bryan Strouse13, Ines Verdon13, Andrew Dye13, Michael Woolliscroft13, Udai Banerji31Freeman Hospital, Newcastle, UK; 2University College Hospital, London, UK; 3Royal Marsden Hospital, London, UK; 4The Christie Hospital, Manchester, UK; 5Velindre Cancer Centre, Cardiff, UK; 6Oxford University Hospital, Oxford, UK; 7The Beatson West of Scotland Cancer Center, Glasgow, UK; 8Sarah Cannon Research Institute, London, UK; 9Guy’s Hospital, London, UK; 10Weston Park Hospital, Sheffield, UK; 11Western General Hospital, Edinburgh, UK; 12Leicester Royal Infirmary, Leicester, UK; 13Sierra Oncology, Vancouver, Canada

InformationFor more information, email [email protected] or visit www.sierraoncology.com

Acknowledgments This study was sponsored by Sierra Oncology. We would like to thank all participating patients and their families. Investigators thank Cancer Research UK, the Experimental Cancer Medicine Centre (ECMC) and the National Institute of Health Research for research infrastructure support.

A Phase 1/2 First-in-Human Trial of Oral SRA737 (a Chk1 Inhibitor) in Subjects with Advanced Cancer Abstract #3094

Dose escalation (unselected)

Dose optimization(unselected)

Phase 2cohorts

Prostate

Ovarian

Non-Small Cell Lung

Squamous Carcinoma(Head & Neck + Anus)

Colorectal

Prospective patient selection using NGS technology

Focus on genetically-defined replication stress-driven patient populations

Dosing Schedule

Day 1 2 3 4 5 6 7

• • • • • • •SRA737

Tumor SuppresorTP53, RAD50...

Oncogenic DriversCCNE1, MYC...

DNA Repair MachineryBRCA1, FANCA...

Replicative StressATR, CHEK1...

SRA737 is a potent, highly selective and orally-bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1).

Chk1 is a serine/threonine protein kinase in the DNA Damage Response (DDR) network that is critically important in reducing elevated replication stress in certain tumor cells.

Replication stress (RS) is manifested by the slowing and stalling of replication forks which results in DNA that is prone to damage. Increased RS results in genomic instability, which affords survival advantages to tumor cells, however, if not properly managed, can result in extensive DNA damage and cell death.

Consequently, tumor cells increase reliance on Chk1 to manage elevated intrinsic RS. It is hypothesized that cancer cells with higher RS may have increased sensitivity to Chk1 inhibitor therapy.

Intrinsic sources of RS can include genetic alterations in tumor suppressors, oncogenes or DNA damage repair genes.

Tumors harboring defects in these functional gene networks are hypothesized to have higher levels of intrinsic RS due to dysregulated cell cycle control, increased proliferation demands and increased genomic instability (Figure 1). This signal-seeking Phase 1/2 study (NCT02797964) was designed to investigate the safety and tolerability of continuous, daily dosing of SRA737, as well as to evaluate preliminary anti-tumor activity in tumors with genetic alterations predicted to confer increased intrinsic RS and Chk1i sensitivity.

Prospective genetic screening was performed to identify and select subjects harboring two or more of these genetic alterations. The study was designed as a broad survey in order to explore the association between various sources of intrinsic RS and SRA737 monotherapy anti-tumor activity and to delineate potential genetic signatures and/or tumor indications that might warrant additional therapeutic investigation.

In the Dose Escalation phase, 18 subjects received SRA737 across 9 dose level cohorts, ranging from 20 to 1300 mg QD. Of these subjects, 3 experienced DLTs (inability to receive 75% of the planned dose); 2 at 1300 mg QD due to gastrointestinal intolerability and 1 at 500 mg BID due to thrombocytopenia. The maximum tolerated dose (MTD) was established at 1000 mg QD or 500 mg BID.

Enrollment of the Cohort Expansion phase was initiated at 600 mg SRA737. Based on overall tolerability, including particularly common gastrointestinal events (nausea, vomiting, and diarrhea), the recommended dose to be employed in the expansion cohorts was determined to be 800 mg QD (RP2D).

In the Cohort Expansion phase, of the 512 subjects prospectively identified, 355 were screened for genetic alterations associated with Chk1 sensitivity. Of these subjects 237 (67%) met genetic eligibility criteria, and 94 were treated in expansion cohorts across six tumor types.

• 107 subjects received treatment with SRA737 acrossboth escalation and expansion cohorts. In the CohortExpansion phase, the largest number of subjects wereenrolled in the HGSOC cohort (n=38) with the nextlargest number in the CRC cohort (n=27).

• Evidence of anti-tumor activity was observed insubjects with HGSOC, colorectal, prostate and non-small cell lung cancer; no RECIST PRs or CRs wereconfirmed, but several noteworthy tumor reductionswere recorded.

• HGSOC appeared as the most sensitive tumor toSRA737 monotherapy in the SRA737-01 study (Figure 3).Although heavily pre-treated (~5 prior lines), the HGSOCcohort demonstrated directionally favorable diseasecontrol (DCR = 54%) with notable maximal tumorreductions of 29% and 27% observed in two patients.

• At the time of the data cut off, durable stable disease(SD) lasting ≥ 4 months was recorded in 22 (21%)

subjects and was observed in all Cohort Expansion tumor types (except HNSCC; 4 subjects) (Figure 2).

• In keeping with the signal seeking objective of thisstudy, tumor responses were further examined with respect to the genetic profiles determined for the tumor types enrolled and treated (Figure 4).

• Among gene networks with > 10 subjects, alterations inseveral genes correlated either positively, or negatively(RAS; Figure 5), with response to SRA737 (Table 1)across multiple indications.

• Notably, genetic alterations in multiple components ofthe FA/BRCA gene network were associated with a71% DCR and DOS of 3.8 cycles (Figure 7). The majorityof subjects with notable responses (tumor reductionand/or > 4 months SD) harbored alterations in either orboth the PI3K (Figure 6) and FA/BRCA gene networks(Table 2).

• Results data cut off: 03 May 2019; Data not final

Characteristic

Overall (Escalation + Expansion)

Tumor types of Interest (Expansion)*

HGSOC (inc. CCNE1 enriched)** CRC** NSCLC mCRPC**

Number of subjects treated 107 38 27 10 15

Age / years (min, max) 64 (38, 86) 60 (39, 86) 64 (38, 79) 66 (50, 75) 68 (54, 80)

Gender (M/F) 46 (43%) / 61 (57%) 0 / 38 (100%) 17 (63%) / 10 (37%) 4 (40%) / 6 (60%) 15 (100%) / 0

WHO performance status (PS0 / PS1 / PS unknown)

39 / 66 / 2 14 / 23 / 1 16 / 10 / 1 3 / 7 / - 4 / 11 / -

Prior systemic therapy regimens; mean (min, max)***

4.2 (1, 10) 4.7 (2, 10) 3.5 (2, 5) 3.2 (2, 6) 5.7 (2, 10)

Treatment delay from consent to C1D1; median (min, max)

61 (9, 329) 59 (11, 329) 74 (10, 154) 86 (15, 314) 63 (9, 296)

Subjects evaluable for target-tumor response****;[# with genetic profile available]

71[64]

24[21]

22[21]

7[7]

9[8]

* In addition to the subjects shown, 4 subjects with HNSCC were enrolled; no SCCA subjects were enrolled** Includes subjects in the Dose Escalation phase concurrently enrolled in Cohort Expansion (3 CRC; 1 HGSOC; 1 mCRPC)*** Prior radiation therapy regimens: n=44**** Subjects with pre- and post-treatment target tumor measurements who received ≥ 75% of total planned C1 dose at ≥ 300mg, or continued on-study after 2 cycles of treatment at any dose levelData cut off: 03 May 2019

The plasma pharmacokinetics of SRA737 were reproducible and generally dose concordant. The Cmin (289 ng/mL) at 1000 mg exceeded that determined in preclinical efficacy models to have anti-tumor activity (100 nM; ca 37.9 ng/mL). All doses ≥ 300 mg QD also exceeded this threshold level.

Treatment-Emergent Adverse Events (TEAEs)

Occurring in ≥ 20% of subjects N=107, n (%)

≥ Grade 3 n (%)N=107, n (%)

Subjects with any TEAE 106 (99.1%) 73 (68.2%)

Diarrhea 73 (68.2%) 2 (1.9%)

Nausea 71 (66.4%) 3 (2.8%)

Vomiting 55 (51.4%) 1 (0.9%)

Fatigue 50 (46.7%) 3 (2.8%)

Decreased appetite 25 (23.4%) 0

Anemia 23 (21.5%) 2 (1.9%)

TEAEs regardless of the investigator’s assessment of causality; Data cut off: 23 March 2019.

Day

-7

to -

4Dose(mg)

Tmax*(h)

Cmax(ng/mL)

Cmin(ng/mL)

AUC0-24h(ng•h/mL)

t1/2(h)

CL/F(L/h)

Vz/F(L)

160(n=1)

4(-)

178(-)

31.7(-)

1,618(-)

13.8(-)

70.0(-)

1,392(-)

300(n=1)

4(-)

353(-)

41.2(-)

3,152(-)

8.6(-)

81.9(-)

1,015(-)

600(n=4)

2(1 - 2)

998(337)

129(49.4)

8,870(3,170)

12.9(1.4)

56.9(20.8)

1,090(516)

800(n=38)

4(1 - 6)

1,884(606)

234(98.2)

18,537(6,056)

10.5(1.8)

39.1(14.9)

596(281)

1000(n=44-45)

4(0.5 - 8)

2,098(805)

289(151)

20,270(7,656)

11.0(1.7)

44.9(22.5)

704(398)

1300(n=3)

2(2 - 4)

3,228(1,320)

466(234)

29,796(11,233)

11.8(3.1)

38.6(19.7)

625(221)

* Tmax reported as Median (min-max)

The Dose Escalation phase employed an accelerated titration design starting at 20 mg SRA737, administered QD orally in 28-day cycles. Incremental dose escalations in single-subject cohorts were followed by a rolling-6 design once SRA737-related ≥ Grade 2 toxicity was observed during Cycle 1.

The Cohort Expansion phase was contemporaneously initiated when circulating plasma concentrations of SRA737 exceeded the minimum effective concentration of SRA737 modelled from murine efficacy studies. Thereafter, experience gained in the ongoing Dose Escalation phase informed dose selection for expansion cohorts.

The Cohort Expansion phase enrolled subjects with genetically defined tumors that harbored genomic alterations hypothesized to confer sensitivity to Chk1 inhibition, which were prospectively selected by

next-generation sequencing (FoundationOne). Subjects with the following tumors were eligible for enrollment: ia) high grade serous ovarian cancer (HGSOC), ib) HGSOC putatively enriched for CCNE1 gene network amplification, ii) colorectal cancer (CRC), iii) metastatic castration-resistant prostate cancer (mCRPC), iv) non-small cell lungcancer (NSCLC), and v) squamous cell carcinomas (headand neck (HNSCC); anus (SCCA)).

This signal seeking Phase 1/2 study was generally conducted in specialty Phase 1 cancer units. Subjects ≥ 18 years of age with an ECOG performance status of0–1, measurable disease (per RECIST v1.1) and archivaltumor tissue (or willingness to consent to a biopsy) wereeligible to participate in the study. For expansion cohorts,subjects must have received at least one prior regimen foradvanced/metastatic disease.

‡ Rate for RAS Wild-Type subjects*Includes FANC A, C, and G**Includes RAD51 and RAD51C

Table 1. Disease Control Rates Vary Across Defined Gene Networks.

RS-driver genes encompassing functional categories (G1/S, Oncogenes, DNA repair genes) were surveyed to identify gene networks and/or individual genes that enriched for sensitivity to treatment with SRA737. Mutations in the RAS gene network were associated with relatively poor response. Alterations in PI3K and FA/BRCA gene networks were associated with favorable disease control. A directionally positive correlation with CCNE is suggested, albeit CCNE network alterations were observed in only a limited number of subjects.

Figure 5. RAS Gene Network Alterations May be Antagonistic to SRA737 Sensitivity.

Mutations in KRAS and NRAS trended toward poor DCR (25%) with 15/20 PDs and an overall average tumor % change of +20%, as well as short duration on study (DOS) of 2 cycles. Given the strong negative correlation with activity, additional pathway/signal searching analyses was performed with exclusion of RAS mutated tumors.

Figure 6. PI3K Gene Network Alterations May Enhance SRA737 Sensitivity.

Alterations in the PI3K gene network (PIK3CA, AKT, PTEN) were associated with a 77% DCR.

Figure 7. FA/BRCA Replication Fork Gene Network Alterations May Enhance SRA737 Activity.

Many of the subjects demonstrating tumor decrease in SRA737-01 harbored one or more genetic alterations in the FA/BRCA gene network, frequently including a secondary mutation in a DDR kinase gene (ATR, PRKDC).

1

10

100

1000

10000

0 6 12 18 24

[SR

A73

7] (

ng

/mL

)

Time (h)

160 mg 300 mg 600 mg 800 mg 1000 mg 1300 mg

Table 2. Summary of Subjects with Notable Responses and their Respective Gene Network Alterations.

Subjects who achieved SD of ≥ 4 cycles and/or best % tumor decrease of > 10% are correlated with their respective gene network alterations. CCNE gene network alterations (DCR=67%) partially overlapped with FA/BRCA subjects but was mutually exclusive with PI3K network alterations.

Tumor Type

Best % Change

Duration on Treatment

(Cycles)

# Lines Prior

Therapy

Gene Network

FA/BRCA CCNE PI3K

HGSOC -29% 4 5HGSOC -27% 2 4mCRPC -21% 4 5CRC -19% 8 3HGSOC -19% 6 6CRC -14% 6 2HGSOC -12% 6 3NSCLC -6% 6u 3mCRPC 0% 9u 2mCRPC 2% 7u 5CRC 4% 6 2NSCLC 4% 5 3CRC 8% 6 3

u Ongoing

Figure 4. Frequency of Gene Network Alterations Across Indications. The heatmap displays the frequency of observed gene network alterations observed in SRA737-01 across treatment cohorts, represented by percent of subjects with gene alterations.

Gene Network HGSOC CRC mCRPC NSCLC

0%

100%

p53 Pathway

G1/S

CCNE

RAS

MYC

PI3K

HR/NHEJ

FA/BRCA

Chromatin

Mismatch Repair

0 1 2 3 4 5 6 7 8 9

! !

Time (m)

SDPDNot Available Non-response EvaluableOngoing

• Overall, these data provide promisingevidence of SRA737 anti-tumor activity andidentify several gene networks associatedwith enhanced SRA737 sensitivity.

• In this first-in-human trial of SRA737monotherapy, the MTD was 1000 mg/day,and based on overall tolerability and PK, therecommended monotherapy dose is 800mg/day. These results highlight the safetyand tolerability of SRA737.

• The signal-seeking study surveyed broadlyacross tumor indications and tumor RS-driver genetics to identify potentialSRA737-sensitive contexts. Preliminaryevidence of anti-tumor activity observedin subjects with HGSOC, colorectal,prostate and non-small cell lung cancersuggests several intrinsic sources of RScontribute to or enhance Chk1 sensitivity.

• The heavily pre-treated HGSOC cohort(~5 prior lines) demonstrated directionallyfavorable disease control (DCR=54%)with notable maximal tumor reductionsof 29% and 27% in two subjects. No cleartrend toward enhanced sensitivity wasnoted with CCNE1 gene amplification;the small subset of subjects enrolled withunambiguous CCNE1 amplifications rendersdefinitive conclusions challenging.

• An evaluation of i) notable tumor volumereductions and ii) longest DOS, revealedthat subjects whose tumors harboredFA/BRCA network mutations displayedthe most favorable outcomes (DCR=71%;DOS=3.8 cycles). The FA/BRCA genenetwork encodes a series of FanconiAnemia and other proteins involved directlyor indirectly in replication fork metabolismand management of RS.

• Importantly, these sensitivity trends wereobserved across multiple indications,suggesting a potential histology-independent sensitization. Similarobservations were made in a clinical studyof SRA737+low dose gemcitabine (LDG)(NCT02797977).

• Within the FA/BRCA pathway, severalnotable tumor volume decreases occurred insubjects harboring two genetic alterations,such as a DDR checkpoint kinase geneor PI3K network. This genetic sensitivitycorrelation, which was also observed in theSRA737+LDG clinical study, suggests thatmultiple mutations may lead to elevatedintrinsic RS and genomic instability, and/orbe a consequence thereof.

• These findings suggest that additionalRS, such as via extrinsic sources, may benecessary to generate durable objectiveresponses with a highly selective Chk1i,as evidenced by anti-tumor activitydemonstrated in the SRA737-02 clinicalstudy, where potentiating LDG wascombined with SRA737.

Figure 1. Intrinsic Inducers of RS Increase Tumor Cell Reliance on Chk1.

RS-driver genes can be divided into several functional categories including G1/S tumor suppressors, oncogenes and DNA repair genes. Research in the DDR field has implicated mutations in G1/S guardian genes, including RB1, TP53 and genes functioning in these pathways, as potentially contributing to intrinsic RS. Certain viral infections that impact these same pathways, e.g. HPV, have also been implicated in increasing cellular RS. In addition, activating mutations in several oncogenes, including MYC, CCNE1 and others, have been suggested to dysregulate replication origin firing and transcriptional programs resulting in elevated RS. Similarly, tumor genetic alterations in certain DNA repair factors, such as those in the Fanconi Anemia and BRCA pathways, have been demonstrated to compromise replication fork stability or repair of damaged forks, exacerbating intrinsic RS.

Figure 3. Directionally Positive HGSOC Cohort Responses.

HGSOC represented the most sensitive indication identified in this study. FA/BRCA gene network alterations were enriched in the HGSOC cohort, particularly in subjects with tumor reduction. Although a cohort of subjects was specifically enrolled to putatively enrich for CCNE network alterations, genetic analysis revealed that only 4/24 subjects had tumors harboring unambiguously positive CCNE1 amplification, resulting in 3 SD and 1 progressive disease (PD). Albeit a very limited dataset, no clear correlation with sensitivity was observed in association with CCNE1 amplification.

Figure 2. Duration on Treatment in SRA737-01. Data shown represent the duration on treatment for all subjects (N=107). A best overall response of SD was seen in 34 (32%) subjects; several subjects (21%) achieved durable SD ≥ 4 months. The median treatment delay from consent to C1D1 to allow for genetic profiling exceeded 2 months, highlighting the challenge of prospective genetic screening using tumor tissue. In a population of subjects with advanced disease (4+ prior lines), this delay in treatment initiation arguably exacerbates underlying disease progression, and is reflected in early drop-outs on study. The identification of both positive- and negative-selection genetic markers as determined in this clinical study may provide a focused ctDNA enrichment strategy for deployment in future clinical studies, potentially expediting prospective enrollment.

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-20%

0%

20%

40%

60%

80%

I n t r ins ic RS Inducers

Oncogenic drivers Dysregulation of replication, transcription/replication collision

MYC* CCNE1* e.g.

Defective DNA damage repairSingle strand breaks, double strand breaks

*Illustrative genes and drivers only

BRCA 1/2*e.g.

Cell cycle dysregulation Loss of G1/S

Defective G1 / S

Checkpoint

TP53*

HPV* e.g.

High RS results in:

Increased reliance on Chk1 in tumor

Genomic Instability

Chk1

regulates RS

Introduction Subject Characteristics and Dose Evaluation Results

Safety

Conclusions

Strategy & Rationale

Methods

300

160804020

600

MED: minimum e�ective dose modeled from preclinical studies

1000

1300

500 mg BID1 DLT

MED

2 DLTs

0 1 2 3 4 5 6 7 8 9

SR

A73

7 D

ose

(m

g)

Cohort

Dose Escalation

SRA737-01, Single Dose

a phase 1/2 first-in-human trial of oral sra737 (a chk1...

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